In the context of this application, having heatshrink properties is taken to mean a material having a transition temperature. Parts made of this material and heated above the transition temperature with no stress applied will assume dimensions that are stable above and below the transition temperature. The part is said to be "heat stabilized". Parts made of this material heated to above the transition temperature, may be stretched to new dimensions then cooled to below the transition temperature while maintained in the stretched condition. The part is said to be "heat recoverable". Then, when the part is reheated to a temperature above the transition temperature with no stress applied, the part will recover to or to its original dimensions. Such materials include polymeric materials which may be cross linked prior to being stretched at above the transition temperature.
Materials having heatshrink properties have played an important role in the development of clamping (or binding) devices used to bind bundles of elongated items, especially cables.
For example, U.S. Pat. No. 3,445,898 to Goodrich describes a heat shrinkable cable clamp comprising a band which wraps around a bundle of one or more cables so that the ends of the band may be bolted together. The band is then heated causing the band to shorten and thereby bind the bundle tightly together. Since a clamp of one size before heatshrink can be used to bind a bundle of cables whose size falls in a range of sizes, the number of clamps required to be kept in stock having various sizes is reduced. A bolt may also be used to fasten the bundle to a supporting surface.
Standard practice for manufacturing the Goodrich clamp begins by cutting a short length from a heat shrinkable polymeric tube. The short length is then collapsed to form a flat band comprising two polymeric strips secured together at each of their two ends. In order to reinforce the clamp near the bolted ends, a flat insert is positioned between the strips at each end and secured by localized heat shrink. The section of the band between the strips is curved into a loop so that one reinforced end of the band lies flat against the other providing that the two ends of the band may be bolted together.
Other inventions utilizing the heatshrink feature have been disclosed including elongated wraparound sleeves for elongated items. The purpose of the sleeves is different from the clamps which are intended to bind bundles of cables whereas the sleeves serve as an overall protective wrap. These patents are presented to further illustrate the uses and constructions as a wrap to which heat shrinkable materials have been applied.
For example, U.S. Pat. No. 4,378,393 to Smuckler discloses an elongated sleeve in which the edges of the sleeve overlap one another to form an elongated seam. Each of the interfacing surfaces that form the seam adjacent to each edge is coated with an adhesive. A tongue is formed along one edge which is engaged with a groove formed in the surface of the mating edge and thereby aligns the interfacing adhesive surfaces when the sleeve is wrapped around the item, prior to heat shrink.
The strength of the seam depends on several factors that are favorable for the application of the device as an elongated wrap. One is that the adhesive interface is subject to a shear stress as the sleeve shrinks with the application of heat rather than a tensile stress normal to the adhesive interface. (Adhesives are well known to possess good shear strength but relatively low peel strength.) The second important factor is that the area of the elongated interface is large which is not the case for the cable clamp comprising a narrow band. Of course, the construction shown in the Smuckler patent does not have an extension that could be bolted to a supporting surface as does the clamp described in the Goodrich patent so that the Smuckler device is useful simply as a protective wrap. Furthermore, it may be noted that the tongue and groove of the Smuckler construction is oriented so that stress in the plane of the adhesive interface generated by heat shrink pulls in a direction that would open the groove permitting the tongue to escape if the tension is great enough. Therefore, the major function of the tongue and groove in this construction is to align the interfacing adhesive coated surfaces rather than add appreciable strength to bonding the two edges of the sleeve. Additionally, the use of adhesive prevents reuseability and repairability. This is a problem when it is desired to unfasten the clamp temporarily for any one of several reasons and then to reapply the clamp.
U.S. Pat. No. 3,455,336 to Ellis discloses a heat shrinkable elongated sleeve in which each of the meeting edges is folded back to form upstanding rails. An elongated metal channel, in which the elongated edges of the channel are bent inwardly toward one another, forms an elongated clip which slides over the rails and secures the edges together.
U.S. Pat. No. 3,654,049 to Ausnit discloses an elongated wraparound heatshrinkable sleeve comprising a sheet in which two parallel elongated hooks are formed along each elongated edge of the sheet and hook onto the hooks of the other edge. A tool is required to fasten the two edges together.
Other patents which illustrate the use of tongue and groove to fasten two elongated edges together include U.S. Pat. No. 3,765,329 to Kirkpatrick which describes a heatshrinkable sleeve wrapped around a cylinder in which the cylinder has a groove formed therein to serve as an anchor for the edges of the sleeve and U.S. Pat. No. 3,910,448 to Evans et al which describes a construction of an enclosure (box) in which joints have a tongue and groove configuration.
The patents discussed in the foregoing paragraphs do not achieve the strength and integrity of closure that is required for many current applications of cable clamps.
For example, although the heat shrinkable clamp described in the Goodrich patent is an improvement over the clamps of bands not having the heatshrinking feature, there continued to be some problems that were not resolved by this early construction. One problem is that, as the clamp (band) tightens around the bundle, a triangularly shaped opening appears where the two ends of the clamp are bolted together, bounded by the bundle of cables and the interior surface of the clamp at the bound ends of the clamp. Therefore, the bundle is not clamped tightly in this region with the result that a cable can become loose. A second problem is that, as the cable clamp shrinks with the application of heat, tearing of the polymeric material may occur where it contacts the more rigid bent metal reinforcement.
Another problem is related to the necessity that, in order to provide an acceptable degree of heat shrinkage of the length of the band, the thickness of the band must be limited below a critical value. The thickness limitation places an upper limit on the achievable strength of the band.
While the Goodrich clamp generally functions entirely satisfactorily for some applications as a cable clamp, there are other situations in which a clamp having greater strength is required.
These and other problems with clamps of the prior art will be apparent to the reader which are resolved by the clamp of this invention.